The present invention relates to a resin-sealed semiconductor device and a method for making the same, and more particularly to a resin-sealed semiconductor device and a method for making the same in which a surface protection layer of a semiconductor chip can be effectively prevented from being broken.
FIGS. 11 and 12 illustrate conventional resin-sealed semiconductor devices. FIG. 11 is a cross-sectional view of a common and conventional resin sealed semiconductor device or a plastic package semiconductor device.
In FIG. 11, a semiconductor chip 1 is mounted on a bed 3 of a lead frame 2 and is connected to an inner lead 2a of the lead frame 2 by bonding wire 4. A mold resin structure 5 completely encapsulates and seals the semiconductor chip 1 and its adjacent wiring area, and an outer lead 2b of the lead frame 2 is shaped as shown, whereby the semiconductor device is obtained.
In FIG. 11, a resin upper thickness A of the mold resin structure 5 above the semiconductor chip 1 is equal to a resin lower thickness B of the mold resin structure 5 below the semiconductor chip 1, so that the mold resin structure 5 is not warped as a whole.
Numerous poor results have been obtained after a heat cycle test when the semiconductor chip 1 has a large size in dimensions as shown in FIG. 12, for the case of the semiconductor device of FIG. 11. The heat cycle test is considered as a thermal environment test equivalent to the use of the semiconductor device under thermal insulation, As the size of the semiconductor chip 1 increases, the passivation layer or a surface protection membrane of the semiconductor chip 1 tends to be broken after the heat cycle test. This problem causes such further problems as the cutting of bonding wires 4 connecting the semiconductor chip 1 and the lead frame 2 and infiltration of impurities or water into the broken passivation layer, resulting in corrosion of the bonding wires.
The breakage of the passivation layer is assumed to be caused as follows.
The mold resin structure 5 having a large coefficient of thermal expansion repeatedly undergoes great expansion and contractions with the change in temperature, whereas the semiconductor chip 1 having a small coefficient of thermal expansion undergoes relatively small expansion and contraction. The mold resin structure 5 applies a force onto the semiconductor chip 1 due to the difference of expansion between them. As the size of the semiconductor chip 1 becomes larger, the force applied by the mold resin structure 5 also becomes greater.